A handover procedure is an important feature of wireless communication systems that provide mobility, so that users can move in the network without experiencing loss of the connection. For example, in cellular systems the user's connection with the network, and thus through the network with other users (user to user(s) connection), is handed over from one cell to another.
Different handover procedures are defined in the standards relating to GSM, for example as defined in the technical specifications relating to the 3rd generation partnership project (3GPP), including 3GPP TS 44.018 (relating to Mobile radio interface layer 3 specification; Radio Resource Control (RRC) protocol, Release 11, version 11.6.0), 3GPP TS 44.060 (relating to GPRS Mobile Station to Base Station interface; Radio Link Control/Medium Access Control (RLC/MAC) protocol, Release 11, version 11.6.0), 3GPP TS 43.129 (relating to Packet-switched handover for GSM Edge Radio Access Network, GERAN, Release 11, version 11.1.0), and 3GPP TS 45.010 (relating to Radio subsystem synchronization, Release 11, version 11.1.0).
A common feature to all these handover procedures is that they will interrupt the user plane data transfer due to data transmission opportunities being stolen or replaced with control signaling. The interruption time is also impacted by the time to switch channel(s) from a serving base station (or serving cell) to a target base station (or target cell), including the associated control signaling. The overall impact to user experience and network performance will depend on how frequent the handovers are performed, and what type of handover is used.
A disadvantage of the existing solutions for handover operations, is that frame losses will result in a perceived degradation of speech quality, especially if the handovers occur frequently. The frame losses occur when the mobile station disconnects from the channel in the serving cell and connects to the channel in the target cell, and in particular before the transmission/reception of speech frames can be resumed.